1. Field of the Invention
This invention relates to catheters and, more particularly, to catheters including an insufflation lumen for supplying humidified gas to a patient.
2. Description of the Prior Art
Catheters are employed for many purposes to provide for passage of fluids to and from the human body. One form of such catheter, more commonly referred to as a tracheal tube, is adapted to be inserted through the oral cavity of a patient and through the trachea to provide for the supply of fluids to the body and for the monitoring of internal conditions in the body and to provide for removal of secretions from within the body. In many cases it is desirable to supply a gas such as oxygen to a patient and it is also desirable that the humidity of the gas so supplied be controlled with reasonable accuracy. Where a gas such as oxygen is supplied to a patient, this is accomplished in many cases by supplying such gas in volumes corresponding to normal respiration through the central aperture, that is, the primary lumen of the catheter, and this over a long period of time was the conventional manner of supplying such gas.
In more recent years there has been a great deal of interest in a new method of ventilating patients, called high frequency jet ventilation (HFJV). In this procedure the gas, instead of being supplied in volumes corresponding to normal respiration, is supplied in small spurts at pressures that are normally higher than those used in conventional ventilation, and the gas is ordinarily supplied through an insufflation lumen provided in the wall of the catheter or through a separate small catheter or needle rather than through the central or primary lumen. Because of the higher pressures employed in HFJV and because of the smaller cross-sectional area of the insufflation lumen compared to that of the primary lumen any significant restriction in the path providing communication to and through the insufflation lumen may cause a significant drop in pressure of the gas as it passes beyond such restriction. This poses a particular problem, as described below, when humidified gas is supplied to a patient, because such a drop in pressure proportionately varies the relative humidity.
The insufflation lumen is ordinarily provided with an opening through the wall of the catheter in the distal region of the catheter for communicating with the lungs of the patient. Further, this lumen is usually formed with an opening in the proximal region of the catheter for receiving a communicating tube, which in turn can be connected to a source of humidified gas. This communicating tube is connected in sealed relationship with the proximal opening of the insufflation lumen in any of a number of ways. For example, it may be connected thereto in the manner set forth in Sheridan et al. Pat. No. 3,625,793, which is assigned to the assignee of the subject application.
In accordance with the process set forth in the Sheridan et al. patent a heated mandrel is inserted into the proximal opening to expand this opening and the communicating tube is inserted into this opening promptly thereafter so that, upon contraction of the catheter material around the proximal opening, a sealing fit is formed with the end of the communicating tube. If the communicating tube is formed of a relatively flexible material the contracting forces around the proximal opening squeeze the communicating tube so as to reduce its internal diameter in the region of the proximal opening. As a result of this restriction there tends to be a significant drop in pressure as the insufflation gas passes beyond this restriction and as a result the relative humidity of the insufflation gas being supplied drops to a significantly lower value. For example, should the gas be supplied at say 2 atmospheres and should the pressure drop to 1 atmosphere beyond the restricted area, the relative humidity of the gas being supplied decreases to approximately one-half its original value. Since the amount of the contraction of the internal diameter of the connecting tube is unpredictable and uncontrollable in such a manufacturing operation the user would be faced with lack of knowledge of the humidity of the gas actually reaching the patient. This is very undesirable.
In lieu of the process described above for connecting the communicating tube to the proximal opening, such connection may be accomplished by means of suitable glue or solvent which acts on the plastic of which the catheter and the communicating tube are formed. In such case it is conventional to first enlarge the proximal opening of the insufflation lumen so as to facilitate insertion of the communicating tube. In this case, when the solvent is applied to the abutting surfaces, the wall of the catheter at the proximal opening tends, because of the elastic memory of the plastic of which it is formed, to return toward its original size. This, as in the above-described arrangement utilizing the process of the Sheridan patent, also results in a restriction of the internal diameter of the communicating tube. This gives rise to the same problem as that just discussed.
One proposed solution to this problem has been to form the communicating tube of a more rigid material so as to resist contraction under the force exerted by the wall of the catheter surrounding the proximal opening and thus to eliminate restriction in the internal diameter of the communicating tube or to substantially limit the amount of such restriction. This, however, gave rise to an additional problem in connection with the primary lumen of the catheter. When such a rigid connecting tube is inserted into the proximal opening it has a tendency to force the wall of the primary lumen inwardly, thereby modifying the internal shape of the lumen at that point and reducing the cross-sectional area of the primary lumen with consequent restriction of flow of fluid therethrough. Further it is important to have a uniform cross-section throughout the length of the primary lumen to facilitate the passage of components, such as suction catheters, therethrough.
By the present invention both of these problems are eliminated and a catheter is provided in which there is no significant restriction of the internal diameter of the communicating tube and in which there is no inward bulge and restriction in the primary lumen.
Accordingly, it is an object of this invention to provide a catheter including an insufflation lumen which facilitates the providing of gas through the insufflation lumen at controlled pressure and relative humidity.
It is another object of this invention to provide a catheter which avoids restriction in the tube for supplying humidified gas from a suitable source to the insufflation lumen.
It is a further object of this invention to provide a catheter construction in which the communicating tube for supplying gas to the insufflation lumen not only has no restriction therein but further does not adversely affect the cross-sectional area of the primary lumen of the catheter.